The end-Cretaceous mass extinction was rather unpleasant

Climate simulation shows how long soot blotted out the Sun.

There are a few hellish episodes in Earth’s unfathomably long history that make even Hollywood’s most bombastic disaster movie look like a sunny picnic. The end-Cretaceous extinction is the most well-known, since it wiped out the dinosaurs (minus the birds, of course) and opened the door for the mammalian revolution—which most human beings regard as generally a good thing.

Though the story is probably familiar, there are still significant questions about exactly what happened during that cataclysm. Many species were seemingly in trouble before that colossal meteoroid crashed into the coastal Yucatan, perhaps partly because of a long-lived series of massive volcanic eruptions in what is now India. This has led some to question whether the impact was as deadly as it's made out to be. But we've also filled in some details of just how the meteoroid impact would mess up the Earth, and these include mind-blowing tsunamis, rampant wildfires, and see-sawing climate effects. So how lethal was the impact?

Further Reading

A team led by Charles Bardeen at the National Center for Atmospheric Research employed a climate model to investigate one major aspect of this story. In many places around the world, there is a thin geologic layer that marks the time of the impact event. It contains soot that apparently blanketed the planet after wildfires kicked it up into the air. (These wildfires would be triggered globally by the heat of debris reentering the atmosphere.) Was there enough soot to black out the Sun?

Several estimates have been made of the total amount of that soot based on the volume that can be found in the rock layer, but these range from 750 billion kilograms to 35 trillion kilograms. The researchers ran several different simulations based on those estimates. In each case, the soot particles are injected high into the atmosphere because soot absorbs sunlight, so it heats up the air around it, causing the air to rise and take the soot with it.

The simulations showed that most of the soot falls out of the atmosphere within a year, but that still leaves enough up in the air to block out 99 percent of the Sun’s light for close to two years, with the poles clearing up fastest. Photosynthesis in the ocean ends once you get to one percent of sunlight, so the authors use this as the threshold for plant life.

Further Reading

That’s two years of perpetual twilight without plant growth, which is probably enough to explain the extinction of plankton species in the ocean (and most things up the food chain from there).

Enlarge/ Simulation results showing percentage of sunlight reaching the Earth surface (colors) in years two, three, and four after the impact. (Note that modern continent positions are used, but things would have looked a little different 66 million years ago.)

And, of course, a biting cold would come with the dim Sun. In the simulation, the average ocean surface temperature drops by as much as 11 degrees Celsius (20 degrees Fahrenheit), and the average temperature on land suffers a 28-degree-Celsius (50-degree-Fahrenheit) drop. Most of the planet’s land area would have been below freezing for the first couple of years. Only a limited area along some coasts and parts of the tropics would escape the frost.

That surface cooling—coupled with the soot-warmed air high above—would drastically slow the water cycle, reducing global precipitation by about three-quarters for six years. Even the monsoons shut down. If you’re keeping track, we’re now talking about a dark, frozen, desert world. Only a very small area of land is bright enough, warm enough, and wet enough for plants to survive.

For organisms that somehow managed to survive through this desolation, conditions could actually have returned to normal pretty rapidly. There’s a sort of critical point as the levels of soot in the stratosphere drop; once it's crossed, the rest quickly clears up. That's because a ton of water vapor would also have risen into the stratosphere with all that soot, and that water vapor acts like a planetary radiator, emitting heat energy to space and accelerating the stratospheric cooling. As the soot level drops below the critical point, less sunlight is absorbed, and the water vapor cools and condenses. It then drops out and takes the remaining soot with it in a matter of months.

In the simulations, that process takes place in year seven, bringing back the sunshine and most of the precipitation. At that point, surface temperatures are only about 5 degrees Celsius below their starting point, and they return to normal over the next decade.

Caveats include the fact that the researchers used a model of the modern climate system, so the map would look a little different with continents in the positions they held 66 million years ago. And they were only able to simulate the soot part of the story. The meteoroid impact itself would have kicked up a serious amount of sulfate aerosols, which scatter enough light to cool the climate but wouldn’t blot out the Sun like soot. A large amount of CO2 would also have been added to the atmosphere, which would mostly manifest itself in long-term warming after the short-term freeze had ended.

How would those things combine with the soot effects? That’s not clear, but it’s interesting that the soot scenario seems bad enough for a mass extinction on its own. It’s hard to imagine that it could have been even worse.

118 Reader Comments

The one unexpected thing I learned from this week's eclipse is that even with 99% of the sun blocked out, it still pretty much seems like daylight outdoors. Not until the very last sliver of the sun's disk disappeared did it become dark, like post-sunset dark. That leads me to question whether some photosynthesizing organisms couldn't survive in greatly reduced sunlight. If there were truly no plant life left, I wonder how anything else could have survived. It seems that there had to have been sufficient "plants," even single-celled ones, that survived in very dim light to provide food for the very limited fauna that also survived.

Interesting, I guess - but there's no way to tell what they actually did since it's hidden behind the PNAS paywall. Yet since this is the National Center for Atmospheric Research, we can be sure this is 100% taxpayer-financed research - so why can't anyone access it?

This has to be the most ridiculous aspect of the Internet - the most interesting valuable information is hidden from all who don't have a academic university log-in, even though almost all that information was generated with taxpayer dollars, all so a handful of publishers can keep collecting their filthy lucre.

Well the good news is we have sufficient technology to survive as a species for a few years like this. The bad news being of course that while the species would survive, probably something like 99% of the population would die from starvation. I hope something like this never actually happens.

I would assume scavenger animals would be the big winners, so thanks be to our late late late late late ancestors not being picky eaters.

There's be enough stuff just dying over time to provide calories for a moderate period of time, I'd think. Insects involved in the decomposition cycle would still have plenty to eat for quite some time, and things that eat those insects would still do well as well....ie small birds and mammals.

Well the good news is we have sufficient technology to survive as a species for a few years like this. The bad news being of course that while the species would survive, probably something like 99% of the population would die from starvation. I hope something like this never actually happens.

Well the good news is we have sufficient technology to survive as a species for a few years like this. The bad news being of course that while the species would survive, probably something like 99% of the population would die from starvation. I hope something like this never actually happens.

It would be a good time to decrease investment in solar panels and increase investment in UV grow lights.

The one unexpected thing I learned from this week's eclipse is that even with 99% of the sun blocked out, it still pretty much seems like daylight outdoors. Not until the very last sliver of the sun's disk disappeared did it become dark, like post-sunset dark.

As far as I'm aware that is an "optical illusion" based on our eyes' ability to adjust to low light situations. When 99% of the sun is blocked, the energy reaching Earth should also be reduced by 99%.

Well the good news is we have sufficient technology to survive as a species for a few years like this. The bad news being of course that while the species would survive, probably something like 99% of the population would die from starvation. I hope something like this never actually happens.

It would be a good time to decrease investment in solar panels and increase investment in UV grow lights.

Several estimates have been made of the total amount of that soot based on the volume that can be found in the rock layer, but these range from 750 billion kilograms to only 35,000. The researchers ran several different simulations based on those estimates. In each case, the soot particles are injected high into the atmosphere because soot absorbs sunlight, so it heats up the air around it, causing the air to rise and take the soot with it.

This paragraph doesn't seem to make sense to me. I find it hard to believe only 35,000 kilograms of soot would block out 99% of solar radiance for 2 years.

The one unexpected thing I learned from this week's eclipse is that even with 99% of the sun blocked out, it still pretty much seems like daylight outdoors. Not until the very last sliver of the sun's disk disappeared did it become dark, like post-sunset dark. That leads me to question whether some photosynthesizing organisms couldn't survive in greatly reduced sunlight. If there were truly no plant life left, I wonder how anything else could have survived. It seems that there had to have been sufficient "plants," even single-celled ones, that survived in very dim light to provide food for the very limited fauna that also survived.

Even if all the plant life on the planet 100% died, you could still have seeds remaining that could grow new plants when the sun and temperature could support it a couple years later. I'm not an expert though, so take that with whatever sized grain of salt you want...

The one unexpected thing I learned from this week's eclipse is that even with 99% of the sun blocked out, it still pretty much seems like daylight outdoors. Not until the very last sliver of the sun's disk disappeared did it become dark, like post-sunset dark.

As far as I'm aware that is an "optical illusion" based on our eyes' ability to adjust to low light situations. When 99% of the sun is blocked, the energy reaching Earth should also be reduced by 99%.

Indeed, and for those in the eclipse zone, it was quite obvious just how much light was being blocked by virtue of the drastic change in temperature well before the totality.

I have to admit that in a lot of ways, I see the whole "they were dying off already, so the meteor didn't do much" argument to be little more than someone saying it didn't matter if the terminal cancer patient undergoing treatment got hit by the bus, they would have died anyway.

Maybe, maybe not.

What seems to be increasingly clear is that although seven years is a pathetically short period of time on a geologic/evolutionary scale, it's more than long enough to kill pretty much everything if there's no food left - which seems to be the case in general (save for those very few, select places where life could still wiggle on).

Didn't much matter that some species were stressed.

Given the focus on that time period, I'm inclined to say that if one were to look as closely at other time periods, there would likely have been other signs of stresses from various causes as well. Climate isn't exactly "stable", though it does tend to resist change. Were one to be around then, and take climate readings, it's likely that the whole "global extinction of 75% of all life" event would be little more than a blip on the thousand year scale in the overall climate (assuming other changes didn't occur, that is). It may have been that there were stresses in the few thousand years leading up to the KT event, but how would they have actually played out over millions of years?

We'll probably never know, but it's moot anyway.

T'was murder most astronomical... The Meteor did it in the Yucatan Peninsula with kinetic energy.

Well the good news is we have sufficient technology to survive as a species for a few years like this. The bad news being of course that while the species would survive, probably something like 99% of the population would die from starvation. I hope something like this never actually happens.

It would be a good time to decrease investment in solar panels and increase investment in UV grow lights.

The one unexpected thing I learned from this week's eclipse is that even with 99% of the sun blocked out, it still pretty much seems like daylight outdoors. Not until the very last sliver of the sun's disk disappeared did it become dark, like post-sunset dark.

As far as I'm aware that is an "optical illusion" based on our eyes' ability to adjust to low light situations. When 99% of the sun is blocked, the energy reaching Earth should also be reduced by 99%.

Indeed, and for those in the eclipse zone, it was quite obvious just how much light was being blocked by virtue of the drastic change in temperature well before the totality.

If we didn't have an atmosphere to reflect and scatter the light falling outside the zone of totality, the difference would be even more apparent. It's the reason for civil/nautical/astronomical twilight.

enough up in the air to block out 99 percent of the Sun’s light for close to two years

Have to wonder how the mammals survived this.

There were primarily smaller mammals around at the time I believe, many of those would have been nocturnal (ie. they operated at night, so the lack of light isn't an issue), as well as subterranean (underground burrows, perhaps with tunnel systems), this would have shielded them from the worst of it, though the mass extinction of most plant-life on the planet would have been very hard on the herbivore species.

The one unexpected thing I learned from this week's eclipse is that even with 99% of the sun blocked out, it still pretty much seems like daylight outdoors. Not until the very last sliver of the sun's disk disappeared did it become dark, like post-sunset dark. That leads me to question whether some photosynthesizing organisms couldn't survive in greatly reduced sunlight. If there were truly no plant life left, I wonder how anything else could have survived. It seems that there had to have been sufficient "plants," even single-celled ones, that survived in very dim light to provide food for the very limited fauna that also survived.

You're missing the fact that during an eclipse only an infinitesimally small part of the earth has 99% of the sun's light blocked. Most of Earth only sees a minuscule diminution of light, and it's over a few hours. There's absolutely no comparison between an eclipse and 99% blockage of sunlight over the entire surface of the earth for two years.

In Carbondale, IL, where I saw the eclipse in totality, there was still plenty of light from the "360° sunset" surrounding us, since the horizon wasn't in totality. What the simulation is reporting is essentially two years of continuous night, everywhere on the planet, with no break whatsoever.

So, it seems that ramming a huge asteroid into our planet is the best solution for global warming.

Technically we just need to start a lot of fires.

Neither would do anything to stop global climate change (at least over the long term). Fires would put more carbon into the atmosphere, which wouldn't precipitate out like soot would. The asteroid's effects, over the long term, would eventually be offset by the increase in atmospheric carbon.

It's not even a stop-gap measure. Of course, if one considered that seven years of no food would pretty much stop civilization from existing, thus ending all Human life, then at least that source of carbon emissions would end, so you may be on to something on a thousand year scale.

But it'd be a Pyrrhic victory for us, at best.

( I know you guys are being sarcastic and lol'd, but given the lengths some folks go to support their rationalizations, they might think it's a good idea, assuming they believed that climate change is happening in the first place.)

The one unexpected thing I learned from this week's eclipse is that even with 99% of the sun blocked out, it still pretty much seems like daylight outdoors. Not until the very last sliver of the sun's disk disappeared did it become dark, like post-sunset dark. That leads me to question whether some photosynthesizing organisms couldn't survive in greatly reduced sunlight. If there were truly no plant life left, I wonder how anything else could have survived. It seems that there had to have been sufficient "plants," even single-celled ones, that survived in very dim light to provide food for the very limited fauna that also survived.

If I recall correctly this is more as a result of human perception than anything. A room that is objectively 1/100 is luminous maybe seems only 1/10 as bright. Humans have a logarithmic perception of changes in brightness.

Did the paper describe what differences might have arisen in their simulation if they had used the continental placements from 66 MY ago? By saying "a little different" are they claiming insignificance?

So, it seems that ramming a huge asteroid into our planet is the best solution for global warming.

Technically we just need to start a lot of fires.

Neither would do anything to stop global climate change (at least over the long term). Fires would put more carbon into the atmosphere, which wouldn't precipitate out like soot would. The asteroid's effects, over the long term, would eventually be offset by the increase in atmospheric carbon.

It's not even a stop-gap measure. Of course, if one considered that seven years of no food would pretty much stop civilization from existing, thus ending all Human life, then at least that source of carbon emissions would end, so you may be on to something on a thousand year scale.

But it'd be a Pyrrhic victory for us, at best.

( I know you guys are being sarcastic and lol'd, but given the lengths some folks go to support their rationalizations, they might think it's a good idea, assuming they believed that climate change is happening in the first place.)

I'd be less worried about people thinking that blowing up the Earth is a good solution and more concerned with people pushing the idea that it's the only effective/most commonly accepted solution and that we really are better off just ignoring the problem instead. That's been a much bigger problem, in my experience.

enough up in the air to block out 99 percent of the Sun’s light for close to two years

Have to wonder how the mammals survived this.

We stood on the shoulders of giants. Er no, we stood on the carcasses of giants. No that's not right either, our rat like ancestors dined on the carcasses of giant dinosaurs. Mmm tasty. You eat your shelter out of a tyrannosaur and live there till it is time to move. A few years later you are king of the world!

enough up in the air to block out 99 percent of the Sun’s light for close to two years

Have to wonder how the mammals survived this.

It's likely a size/food need thing.

Mammals at the time were generally very small. The amount of food needed for one dinosaur to survive a day would likely have fed a small army of mammals for a week.

Mammals are also warm blooded, which helps regulate their body temperatures. Dinosaurs are warm-blooded, but were generally much, much, much larger (at least the ones who died off). This is why birds aren't generally exceptionally huge (on a dinosaur scale). Their evolutionary predecessors survived for the same reason mammals did. They were small and required less food to survive.

There were likely other nuances involved, but, again, nuances. When it comes to the length of time one can survive, the less food they have to eat to keep going, the longer they'll live in a time when food supplies are limited.

Well the good news is we have sufficient technology to survive as a species for a few years like this. The bad news being of course that while the species would survive, probably something like 99% of the population would die from starvation. I hope something like this never actually happens.

It would be a good time to decrease investment in solar panels and increase investment in UV grow lights.

Which would be powered how?

coal, nuclear, natural gas, wind, tidal harnesses, enslaving the surviving rodent population to run on little wheels... take your pick.

I am partial to the future of electricity being powered by a huge warehouse full of hamsters running on wheels myself; seems the most logical solution to the problem.

Several estimates have been made of the total amount of that soot based on the volume that can be found in the rock layer, but these range from 750 billion kilograms to only 35,000. The researchers ran several different simulations based on those estimates. In each case, the soot particles are injected high into the atmosphere because soot absorbs sunlight, so it heats up the air around it, causing the air to rise and take the soot with it.

This paragraph doesn't seem to make sense to me. I find it hard to believe only 35,000 kilograms of soot would block out 99% of solar radiance for 2 years.

I just checked the paper and it is a typo in the article. They modeled 3 injections of carbon, 15,000 Tg, 35,000 Tg, and a 'measly' 750 Tg (where Tg is 10^12 grams or 1 billion kg) as some papers have suggested this smaller amount.

The one unexpected thing I learned from this week's eclipse is that even with 99% of the sun blocked out, it still pretty much seems like daylight outdoors. Not until the very last sliver of the sun's disk disappeared did it become dark, like post-sunset dark. That leads me to question whether some photosynthesizing organisms couldn't survive in greatly reduced sunlight. If there were truly no plant life left, I wonder how anything else could have survived. It seems that there had to have been sufficient "plants," even single-celled ones, that survived in very dim light to provide food for the very limited fauna that also survived.

Even if all the plant life on the planet 100% died, you could still have seeds remaining that could grow new plants when the sun and temperature could support it a couple years later. I'm not an expert though, so take that with whatever sized grain of salt you want...

No, you're right. Seeds can last from a couple of years to decades, or even centuries under the right conditions. And they are pretty enthusiastic about sprouting as soon as conditions trigger it.

Edit: and a lot of long-lived plants can go dormant for years, and resprout from rootstock when conditions are right.

Well the good news is we have sufficient technology to survive as a species for a few years like this. The bad news being of course that while the species would survive, probably something like 99% of the population would die from starvation. I hope something like this never actually happens.

It would be a good time to decrease investment in solar panels and increase investment in UV grow lights.

Which would be powered how?

coal, nuclear, natural gas, wind, tidal harnesses, enslaving the surviving rodent population to run on little wheels... take your pick.

I am partial to the future of electricity being powered by a huge warehouse full of hamsters running on wheels myself; seems the most logical solution to the problem.

Plus we get tiny little hamster nuggets when they're done on the wheels and there's new generation of fresh hamsters to enslave.